Resole resins, commonly referred to as one-step phenolic resins, are generally produced by polycondensing phenols such as phenol and cresol with aldehydes such as formaldehyde and acetaldehyde in the presence of basic catalysts such as aqueous ammonia, organic amines or sodium hydroxide.
The production of novolak resins, referred to as two-step phenolic resins, is generally accompanied by thermosetting with the aid of a cross-linking agent such as hexamethylenetetramine. On the other hand, resole resins having a high methylol group content in the molecule are inherently thermosetting and can be directly cured. Because of their extremely high reactivity, resole resins are usually manufactured as aqueous or methanol solutions with a solids content ranging from about 50 to 60 wt % and are stored as such. Recovery of resole resins in a stable particulate or powder form is generally considered to be difficult.
Various approaches have been disclosed to produce resole resins in a stable solid form. For example, U.S. Pat. Nos. 3,823,103, 4,026,828, 4,039,525 and 4,206,095 disclose the production of particulate resole resins by emulsion polymerizing phenols and formaldehyde in the presence of both a basic catalyst (e.g., ammonia) and a protective colloid such as gum arabic (U.S. Pat. No. 3,823,103), gum ghatti (U.S. Pat. No. 4,026,828) or hydroxyalkylated guar (U.S. Pat. No. 4,039,525). The characteristics of the resole resins prepared by these methods and the possible applications in which such resins can be used are reported in G. L. Brode, T. R. Jones, S. W. Chow, CHEMTECH, November, 676-681 (1983), A. M. Regina-Mazzuca, W. F. Ark and T. R. Jones, Ind. Eng. Chem. Prod. Res. Dev., 21, 139 to 141 (1982) and G. L. Brode, P. W. Kopf and S. W. Chow, Ind. Eng. Chem. Prod. Res. Dev., 21, 142-145 (1982).
Japanese Patent Publication No. 42077/78 discloses a process wherein a phenol is condensed with formaldehyde using a basic catalyst in the presence of a nitrogen-containing compound such as ethylenediamine, and to the resulting condensate, a hydrophilic organic polymer such as gelatin, casein or poly(vinyl alcohol) is added to further continue the reaction so as to produce a resole resin in either a particulate or powder form.
Japanese patent application (OPI) No. 88995/79 (corresponding to U.S. Pat. No. 4,182,696) (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") describes a process for producing a resole resin by reacting a mixture of formaldehyde, phenol and an amine compound such as hexamethylenetetramine in an aqueous medium with a filler having a reactive group capable of chemically bonding to a phenolic resin in the presence of a protective colloid.
In each of the prior art methods described above, a hydrophilic organic polymer compound is used as an emulsion stabilizer and the resulting resole resin inevitably contains such a hydrophilic compound. Therefore, moldings of such resin have relatively poor properties in terms of, for example, resistance to heat and moisture. Furthermore, the resin particles have a tendency to sinter either during drying or during storage.
In order to solve these problems, Japanese patent application (OPI) No. 177011/82 (corresponding to U.S. Pat. No. 4,414,378) discloses a method of producing a solid, thermosetting phenolic resin as fine particles by reacting a phenol with a molar excess of formaldehyde (8 to 10 mols per phenol) in the presence of an acid catalyst. However, the resole produced by this method not only cures slowly but also has so poor flow characteristics that its molding properties are impractically low.
As a final problem, the flame retardancy of phenolic resins is relatively low and needs further improvement.